1. Field of the Invention
The invention relates generally to chip or die handling during fabrication of microelectronic circuit chips and specifically to a method and apparatus for facilitating the removal of circuit chips from wafer handling tape after separation operations such as sawing or scribing.
2. Description of the Prior Art
Current conventional practice in the manufacture of circuit chips most commonly involves the fabrication of semiconductor wafers which are usually 2 to 6 inches in diameter and approximately 0.010 inch to 0.020 inch thick. Formed on one surface of the wafer is a grid of semiconductor devices comprising individual circuit elements which are to be separated into discrete circuit chips or dies. These individual circuit elements typically vary in size from 0.010" to 0.50" square. Such circuit chips vary tremendously in circuitry and function but are generally processed similarly once formed on a wafer. In particular, the circuit chips are separated with a diamond saw or diamond scriber after the wafer has been mounted to a piece of wafer handling tape such that the wafer is fixed during the sawing operation and the chips thus separated from each other are held in place after completion of the sawing operation. The tape bearing the wafer can be affixed to a film frame either by hand or with a wafer film frame mounting device as is conventional in the art. After separation of the circuit chips from each other, the individual chips must be removed from the tape without damage to the chips. Conventional practice has included the use of a wafer expanding device which facilitates the separation of the circuit chips from each other. The circuit chips are then manually removed from the tape after expanding through the use of tweezers, vacuum pencils, etc. or through the use of devices such as die ejector systems. The manual techniques including the use of tweezers suffer from the disadvantages that damage often occurs to the circuit chips simply through mechanical contact between the tweezers and the circuit chips. The use of die ejector systems also has disadvantages including the transfer of small spots of tape onto the back of the circuit chips once the ejector needle of the ejector system becomes dull through use. Many ejector systems impact the back of the circuit chip with such force that discontinuities can be formed in the back surface of the chip.
Prior attempts to address the problems noted above include those methods and apparatus described in U.S. Pat. Nos. 4,667,944 and 4,711,014 to Althouse. As described in these patents, Althouse provides a fabric having spaced fiber cross overs used in association with a chip-bearing tape with vacuum forces being used to facilitate removal of chips from the tape. Chough et al., in U.S. Pat. No. 3,809,050, mounts a wafer for dicing with a vacuum plate having individual apertures which apparently align with each chip after dicing. Chough et al. do not provide the ability to pull portions of the tape contacting each chip away from the chip for facilitating release of the chip from the tape. Wheeler, in U.S. Pat. No. 4,433,835, and Avedissien et al., in U.S. Pat. No. 4,472,218, teach the use of vacuum to hold either undiced or diced wafers in place for processing operations. Avedissien et al. remove chips from a tape through the use of a punch-like needle which comes up from beneath the tape and contacts the chip to separate the chip from the tape. As such, Avedissien et al. describe the use of die ejector systems having problems as are noted above. In U.S. Pat. No. 4,664,739, Aurichio describes heating of a wafer/adhesive film assembly prior to dicing. However, Aurichio does not utilize his heating step in a manner which would facilitate removal of circuit chips from handling tape. In U.S. Pat. Nos. 3,851,758 and 3,915,784, Makhijani et al. utilize a bond releasing fluid for removing chips from a tape. Beltz et al, in U.S. Pat. No. 4,466,852, also utilize a fluid for dislodging chips from a tape. Prior art similar to that noted above can also be found in U.S. Pat. Nos. 3,681,139 to Jannett et al. and 4,395,451 to Althouse. While the methodology and apparatus described in the aforesaid patents are directed in certain respects to the problems addressed by the present method and apparatus, the prior art including the art represented by the aforesaid patents does not fully address the problems noted above relative to the removal of circuit chips directly from wafer handling tape or other handling tape without damage to the circuit chips. The present method and apparatus greatly facilitates removal of circuit chips from such tape both rapidly and without damage to the circuit chips. Further, practice of the present invention allows elimination of certain steps conventionally employed in the removal of chips from tape and also eliminates the need for apparatus utilized in the practice of these steps. Accordingly, the invention provides method and apparatus which facilitates rapid removal of circuit chips from wafer handling tape and similar tapes with reduced damage to the circuit chips and at lower cost due to the elimination of certain presently conventional processing steps and the apparatus necessary for practice of these processing steps.